In stencil printing a filled porous sheet is opened up where it is desired to make an ink flow for imaging; no ink can pass through unopened, blocked areas. Stencil printing includes both screen process printing and mimeograph duplicating. Stencil screens can be made of photoresists. For example, gelatin can be coated on a screen, sensitized by dichromate solution, dried, exposed and washed out to give an imaged screen. Ink can pass through where light has not struck. In mimeograph duplicating, imaged stencils consist essentially of ink-impervious coatings cut to expose a permeable sheet that permits ink to pass through. The stencils are wrapped around a rotating drum of a duplicator. This drum is perforated to permit ink brushed through it to pass to the stencil to image paper fed against the stencil on the drum.
In general, the processes for producing stencils are costly and time consuming. In addition, with existing stencils, ink tends to spread laterally beyond the image perforations by capillary action after extended printing, so as to ink the non-imaged areas. It is to these problems that this invention is directed.